How To Wire A 4 Channel Amp To Front And Rear Speakers

Using an amplifier with new speakers is an absolute must if you want to get the most out of your sound system. In this article, I’ll show you how to hook that amp up to your front and rear speakers and tell you how to get it just right so you get high quality sound from your gear.

Trying to get the best sound out of your car audio system can at first seem like a daunting task, especially if you’re not used to working with electronics. Thankfully, upgrading your speakers and amplifier is a pretty straightforward process and you can save a lot of money installing the parts yourself.

The Benefits Of Upgraded Speakers And Amplifiers

The basic stereo system your car comes with is not that great when it comes to delivering quality, power, and volume. Upgrading your car’s amplifier will supply your new speakers with that much-needed power boost with less distortion than a preinstalled amp inside a factory stereo ever could.

You almost certainly won’t be pushing an upgraded amp to or beyond its capabilities, meaning your sound will come through clearer. And, on top of that, you’ll be able to get a lot more volume with minimal distortion. With a better, higher-quality amplifier in your system, you’ll notice the difference between factory-installed speakers and any upgrades you choose.

What Is A 4 Channel Amp?

A 4 channel amplifier is a device that increases a standard/weak audio input to drive more powerful audio signals to four channels or speakers. The difference between the more common 2 channel amp and a 4 channel amp is, as you might have guessed, the number of channels. A channel is just an external connection at the back of the amp. Each channel usually has one speaker connected. Unless it is bridged – in which case the two channels are use for one speaker to double the power output of the single channel.

With a 4 channel amp, you can save a bit of space and money. Instead of running two separate 2 channel amps, you can get the job done with just one 4 channel amplifier.

How Many Speakers Can I Hook Up To A 4 Channel Amp?

Having four channels instead of two means that you can use those two extra channels for two more speakers or, if you “bridge” them, using their combined power for a subwoofer. Whereas a 2 channel amp can only support either two speakers or one subwoofer with the amp in “bridge” mode, a 4 channel amp supports either four speakers or two speakers and a subwoofer.

Do You Need Two RCA Cables For A 4 Channel Amp?

Most amp wiring kits only come with one RCA cable. This is because the most common amplifiers used in car audio systems have been 2 channel amps. Because you have two more channels, you’ll need a second RCA cable instead of just the one that most amp wiring kits come with.

Before You Begin

Hooking your 4 channel amp up to your speakers is a relatively straightforward process. That being said, it’s best to make sure you have everything planned and prepared before you get started so you don’t have any surprises or get most of the way through and realize you forgot a wire. Let’s take a look at what you’ll need to prepare.

Make A Plan

Before you start hooking things up, make sure you’ve planned out how you’re going to install your amp. It’s best to figure out the route you’ll take before diving in so you can keep it all straight and make the installation easy and efficient.

You should also make a list of what equipment, materials, and tools you’ll need for your project. Just jotting this down on a list somewhere can save you a major headache later in case you misplace something. That way, you’ll be able to find what you need quickly without wondering whether or not you picked it up in the first place.

Wire And Tools Required

As I mentioned before, most amp wiring kits are designed for 2 channel amps. Because we’re working with a 4 channel amp, you’ll need to make sure you really have everything you need before getting started.

If you’re looking into an amp wiring kit, or if you want to put one together yourself, you’ll want to make sure you get the right tools for your installation. This will vary slightly from a typical amp wiring kit because it’s a 4 channel amp.

Here is what you should look for in a good 4 channel amp wiring kit:

  • Two high-quality 18’ RCA cables
  • One high-quality remote wire
  • Ground wire
  • A positive wire with good, stranded conductors of about 18’ length
  • Crimp ring terminals
  • A fuse holder and fuse
  • Zip ties

Some amp wiring kits come with speaker wire, or you can purchase it separately. The amount of speaker wire varies a little depending on the installation type you’ll be performing. When it comes to gauge, though, go for either 18 gauge or 16 gauge speaker wire regardless of which installation you’ll be doing.

As a rule of thumb, it’s best to have a little more speaker wire to work with than may be strictly necessary. This way, you have a little leeway in case you need to work around something in your car’s specific make and model that a standard kit’s length may not account for.

Here’s what you’ll need if you’re working with a factory radio without RCA inputs:

  • Your 4 channel amp
  • An amp wiring kit as described above (RCA cables not necessary)
  • 120’ of speaker wire (a little extra is preferred)
  • 25 (or more) wire crimp connectors
  • 100 (or more) 6” wire ties
  • Electrical tape
  • A crimper tool
  • Cutting pliers
  • A digital test meter for measuring voltage

Here’s what you’ll need if you have RCA inputs:

  • Your 4 channel amp
  • An amp wiring kit as described above (with two 18’ RCA cables)
  • 120’ of speaker wire (a little extra is preferred)
  • 25 (or more) wire crimp connectors
  • 100 (or more) 6” wire ties
  • Electrical tape
  • A crimper tool
  • Cutting pliers
  • A digital test meter for measuring voltage

Installation

There are two ways to install a 4 channel amp and it depends on whether or not you’re working with a factory-installed stereo. Factory radios do not have RCA inputs, which makes things differ ever so slightly from if you were working with RCA connections. I’ll go over both installation types here.

Installation Type A: Factory Radio With No RCA Inputs

If you’re working with a factory stereo that has no RCA inputs, you’ll need to purchase either a line level converter or make sure your amp has speaker level inputs.

Personally, I’d recommend getting a line level converter regardless, if it’s reasonable to do so. This is because it makes the process of upgrading your stereo in the future quite a bit simpler. You’ll already have the RCA cables hooked up to your amplifier and can just plug them in to your newer, better stereo.

Line Level Converters

[Image suggestion: line level converter]
A line level converter allows you to convert speaker level inputs into RCA inputs. They take the signal from your stereo, converting it into a signal that your amp can use via RCA connections. This is incredibly useful if your amp for some reason doesn’t have speaker level inputs.

Even though a line level converter might seem like a simple piece of technology, make sure you still buy a high quality device. If you settle for less, the conversion of that audio signal might not be up to par, resulting in sound distortion or other audio issues.

Speaker Level Inputs

Speaker level inputs are pretty common on modern amplifiers. This saves you the trouble of purchasing a line level converter, which saves you money as well as a step in installation.

Thankfully, they’re straightforward to hook up, as well. There should be a “harness” included, where you simply connect the positive (+) and negative (-) wires for each speaker channel to the harness. Then, you just plug the harness into the speaker level inputs on your amplifier.

Installation Type B: RCA Connections

RCA connections, sometimes also called line-level connections, are the preferred way to get signal connected to your amplifier. They offer a lower-noise connection than speaker-level adapters do and are a bit simpler in terms of installation.

As I mentioned above, you’ll need two RCA cables for a 4 channel amplifier. Each RCA cable will have two signal channels, left and right for your front speakers and left and right for your rear speakers.

Speakers

You want to make sure the amplified signal you get from your new amp gets to your speakers, so you want to make sure they’re wired correctly. One way to make this a little easier on yourself is to run the speaker wires back to the area around the harness on the back of your stereo. That way, all of your car’s speaker wires will be accessible in one place.

We won’t be using the speaker wires coming from the stereo, regardless of if that stereo is old or new. This is because we’re diverting the signal to the amplifier instead. If you want, you can either cut the speaker wires on the stereo or tape them up and out of the way.

Connections

Signal Wiring

If you’re using speaker-level connections, it’s best to connect that wire near the stereo and then run the wiring back towards your amp as one bundle. This keeps things neat and makes installation all the easier.

You’ll need eight lengths of wire: four pairs of wire for the four channels. To get the rough length you’ll need, measure a length of wire from the radio to where the amp will be installed, allowing a little extra to account for any curves and paths the wire might have to take through your car’s interior.

With speaker-level connections, I’d recommend using crimp connectors and crimp wire for a secure connection. Factory stereos will have color-coded wiring, so be sure to find that. If you’re unsure, you can always consult online sources to double check.

RCA Cables

RCA cables are a little simpler than signal wiring with speaker-level connections. If you’re using a line-level converter or can simply use RCA cables as-is, connect the cables to the corresponding front and rear inputs. To keep track of your cables, you might want to mark or tape which are the front and/or rear cables.

2 Channel RCA Jacks

[Image suggestion: two-channel stereo diagram]
If your stereo itself only has two channels but you’re using a 4 channel amp, you can still connect your stereo to the amplifier. It only requires a minor addition: Y-adapter cables.

A Y-adapter allows one RCA jack to be split into two, allowing you to connect your RCA cables as described above with no need to complicate things. With the technology we have now, using a Y-adapter will cause no quality loss, either, meaning you can do this without worry.

Remote-On Amp Wire

Find a +12V wire that has power when your ignition is in the “accessory” or similar position but turns off with your car’s key. This is the wire you’ll use for your remote-on wire. All you need to do to install it is connect the wire to the radio and bundle it with your speaker wires.

The Amplifier

Let’s get into the installation of the amplifier itself. In most cases, you’ll want to install your amp in the trunk or rear of the vehicle with your speaker-level connections near the radio or center console. This is the typical setup, and one that allows for the most flexibility with further upgrades.

1. Route the positive battery wire to the engine compartment.

This will probably be the trickiest part of the installation process. You’ll want to hide the wire underneath the carpet or interior trim, but that’s not the tricky part.

The tricky part is getting the wire into the engine compartment. This can usually be done by finding either a gap, hole, or grommet to feed the wire through. It might take some searching, but your car will have at least one of those options.

2. Connect the positive wire and the fuse holder.

Trim half an inch of insulation from each end of the wire and put the fuse holder on the exposed bit of the positive wire. Use a crimp ring terminal and the crimp tool to secure it.

For safety reasons, make sure the fuse holder is near the battery with about a foot or less of wire in between. This way, there’s not much wire that could be involved without fuse protection in the event of a short-circuit. Don’t use lug terminals instead of crimp terminals, the safety risk just isn’t worth it.

3. Connect the positive wire to the battery.

Make sure the battery area is clean and clear of corrosion, then affix the positive wire using a crimp terminal to fasten it to a battery clamp bolt/stud. To hold it in place, zip tie the wire to other nearby wires or hoses.

4. Establish a grounding connection.

Connect the ground wire from the amp to metal near where the amplifier is going to be mounted. If possible, and if one’s nearby, a factory ground wire is a great place for it. Connect it using either another crimp ring terminal or a drill and self-tapping screw.

5. Route the wires to the amplifier.

Bundle your power wire and other cables together using zip ties. Then run the wires along the same path back to your amplifier. Keeping them together like this will save you a major headache if you upgrade or repair anything in the future.

6. Mount the amplifier.

Most people pick one of two ways to mount their amplifier in their car: either to the subwoofer box itself (if a subwoofer is involved) or to a board they securely attach to the car. I’d recommend making an amp mounting board, as it’ll save your amp from the direct vibrations of a subwoofer.

Making an amp mounting board is simple and straightforward, thankfully. All you need is to get some speaker box carpet or other dark fabric (think JoAnn Fabrics or a similar store) and a board. Affix the carpet to the board, then mount the amp to the board using either brackets or car stereo straps.

7. Connect the wires to the amp.

[Image suggestion: diagram of amp terminal connections]
Make sure the power is turned off and the power wire fuse is removed before connecting anything. Once you’ve made sure of that, you’re in the home stretch.

Connect each wire to the corresponding terminal on your amplifier, making sure the connections are secure and there’s no stray wires in the way. If you’re using speaker-level connections from a factory stereo, this is when you’d connect those, as well.

Setting Up Your Amp

Now that you’ve installed the amplifier, it’s time to make sure everything works and get your amplifier itself set up and ready for use. Make sure the power fuse is in, turn on the ignition, and turn on your stereo.

If you don’t hear any sound and the amplifier’s power light isn’t on, check for any potential issues. This is another place that digital meter will come in handy, as test lights don’t always tell you what you need to know.

There are generally three easy-to-fix reasons your amp might not turn on: a bad grounding wire/connection, an issue with the fuse or fuse holder, or the remote-on wire’s voltage is too low (or not +12V at all).

Setting The Crossovers

Now that your amp is hooked up and on, it’s time to set things so you get the sound you want out of your system. Using the high-pass crossovers allow for higher volume with minimal distortion, so it’s important to make sure they’re set correctly.

For the front and rear channels, make sure the crossovers are set to high-pass. Then, if there’s a control for them, set it somewhere around 50-60Hz. This should be a good spot to get good quality, and if there isn’t a control they should be already set well.

Test And Tweak

The rest of the process really boils down to testing and tweaking your equipment to get it just how you’d like it to sound. Play the kind of music you usually listen to and adjust the settings for bass, treble, gain, and so on as you’d like.

Summary

I know that this process, at a cursory glance, has a lot to it. While it might seem like a lot to digest, however, most of it is thankfully straightforward and easy to do on your own. Even if you’re new to the world of car audio, upgrading your system is completely doable.

Making sure you’re thorough and keep track of your parts saves you from any potential headaches, and your ears will thank you for it.

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